Lead overlay bottom spin valve with improved side reading

ABSTRACT

In bottom spin valves of the lead overlay type the longitudinal bias field that stabilizes the device tends to fall off well before the gap is reached. This problem has been overcome by inserting an additional antiferromagnetic layer between the hard bias plugs and the overlaid leads. This additional antiferromagnetic layer and the lead layer are etched in the same operation to define the read gap, eliminating the possibility of misalignment between them. The extra antiferromagnetic layer is also longitudinally biased so there is no falloff in bias strength before the edge of the gap is reached. A process for manufacturing the device is also described.

This is a division of patent application Ser. No. 10/093,107, filingdate Mar. 7, 2002, now U.S. Pat No. 6,779,248, Lead Overlay Bottom SpinValve With Improved Side Reading, assigned to the same assignee as thepresent invention, which is herein incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The invention relates to the general field of read heads for magneticdisk systems with particular reference to the problem of controllingwidth of area read.

BACKGROUND OF THE INVENTION

The principle governing the operation of the read sensor in a magneticdisk storage device is the change of resistivity of certain materials inthe presence of a magnetic field (magneto-resistance).Magneto-resistance can be significantly increased by means of astructure known as a spin valve. The resulting increase (known as Giantmagneto-resistance or GMR) derives from the fact that electrons in amagnetized solid are subject to significantly less scattering by thelattice when their own magnetization vectors (due to spin) are parallel(as opposed to anti-parallel) to the direction of magnetization of thesolid as a whole.

The key elements of what is termed a top spin valve are, starting at thelowest level, a free magnetic layer, a non-magnetic spacer layer, amagnetically pinned layer, and a topmost pinning layer. Invertedstructures in which the free layer is at the top are also possible (andare termed bottom spin valves). Only the lowest layer of a bottom spinvalve is seen in FIG. 1—antiferromagnetic layer 11.

Although the layers enumerated above are all that is needed to producethe GMR effect, additional problems remain. In particular, there arecertain noise effects associated with such a structure. As first shownby Barkhausen in 1919, magnetization in a layer can be irregular becauseof reversible breaking of magnetic domain walls, leading to thephenomenon of Barkhausen noise. The solution to this problem has been toprovide operating conditions conducive to single-domain films for MRsensor and to ensure that the domain configuration remains unperturbedafter processing and fabrication steps as well as under normaloperation. This is most commonly accomplished by giving the structure apermanent longitudinal bias provided, in this instance, by two opposinglayer 16 which are separated by gap 13 (FIG. 1). Examples of hard biasmaterials include Cr/CoPt or Cr/CoCrPt (where Cr is 0–200 Å), CoPt orCoCrPt (100–500 Å). Also seen in FIG. 1 is capping layer of 17 of Ta orRu with a thickness of 1–30 Å.

As track density requirements for disk drives have grown moreaggressive, GMR devices have been pushed to narrower track widths tomatch the track pitch of the drive and to thinner free layers tomaintain high output in spite of the reduction in track width. Narrowertrack widths degrade stability as the device aspect ratio startssuffering. Thinner free layers have traditionally degraded stability andincreased the asymmetry distribution across the slider population. Thethicker hard-bias that is typically used to overcome stability concernsassociated with the junction also results in amplitude loss due to thefield originating from the hard bias structure. Side reading, which isattributable to any deviation of the head microtrack profile from asquare, also gets worse with narrower track widths

One approach that has been developed by the industry to overcome some ofthese stability concerns has been to use the lead overlay design shownin FIG. 1. In this design, track width is defined by the separation 18of conductor leads 12 rather than by the hard bias separation 13. Thelead overlay design moves the track edges, which are in part the causeof the instabilities, away from the current carrying region.Furthermore, the device has a more favorable aspect ratio, furtherenhancing stability. One remaining concern with such a device is whetheror not it improves side reading. Although there is no substantialcurrent in the area under the leads (overlap region), the region isstill magnetically active and may transmit flux to the center of thedevice. The field due to the hard bias plugs gradually decays startingfrom the hard bias edge reaching a minimum at track center.

The two lines marked as 15 a that extend under the leads a shortdistance from the bias plugs 16 represent the dead zone which is themagnetically inactive region between the wider physical width and thenarrower magnetic width. Because of improper scaling (very high trackdensity relative to linear density), the dead zone has become negative.i.e. the physical width has become narrower than the magnetic width.

A routine search of the prior art was performed with the followingreferences of interest being found:

-   -   In U.S. Pat. No. 6,275,362, Pinarbasi shows a bottom SV process.        In U.S. Pat. No. 6,292,335B1, Gill disclose a bottom SV process        without a hard bias while in U.S. Pat. No. 6,222,707B1, Huai et        al. reveal a related bottom SV process. U.S. Pat. No.        6,221,172B1 (Saito et al.) and U.S. Pat. No. 6,219,208B1 (Gill)        are related SV MR patents.

SUMMARY OF THE INVENTION

It has been an object of at least one embodiment of the presentinvention to provide a magnetic read head in which the physical and themagnetic read gaps have essentially the same value.

Another object of at least one embodiment of the present invention hasbeen to reduce side reading in the lead overlap region, particularly fornarrow track widths.

Still another object of at least one embodiment of the present inventionhas been to reduce misalignment between the lead overlay mask and thehard bias plugs mask.

A further object of at least one embodiment of the present invention hasbeen to provide a process for manufacturing said device based onconventional bottom spin valve and contiguous hard bias manufacturingtechniques.

These objects have been achieved by inserting an additionalantiferromagnetic layer between the hard bias plugs and the overlaidleads. This additional antiferromagnetic layer and the lead layer areetched in the same operation to define the read gap, eliminating thepossibility of misalignment between them. The extra antiferromagneticlayer is also longitudinally biased so there is no falloff in biasstrength before the edge of the gap is reached. A process formanufacturing the device is also described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the upper portion of a bottom spin valve, includingoverlaid leads, as is typical of the prior art.

FIG. 2 illustrates how the device of FIG. 1 may be improved to providenarrower read width.

FIG. 3 is an alternative embodiment of the device shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

We note that once the hard bias field is below a critical value, thepermeability of the free layer is adequate to conduct flux to the centerof the device. Our approach to preventing additional side reading and tosharpen the microtrack profile has been to pin that part of the freelayer that is directly under the lead overlay by the use an additionalantiferromagnetic layer, shown as layer 21 in FIG. 2, providing exchangealong the track width direction. The value of this extra pinning layercould be as low as 50–100 Oe to accomplish the microtrack profilesharpening although higher values of pinning could also be utilized. Theexchange provided by antiferromagnetic layer 21 at track edges adds auniform field onto the field generated by the hard bias plugs 16 in thelead overlap region, ensuring a stiff sensor until the intended activearea of the sensor is reached. As can be seen, this has the effect ofextending the dead zones 15 b all the way to near the edges of theleads.

We note further that this design can be expected to alleviate some ofthe alignment tolerances associated with this type of design by allowingthe use of hard bias plugs that are further apart than is possible withcurrent art designs since the added antiferromagnet is self aligned tothe leads and reduces the response of the sensor under the leads.

Referring now to FIG. 2, we begin a more detailed description of theprocess of the present invention. As this description unfolds, thestructure of the present invention will also become apparent. Theprocess begins with the provision of a bottom spin valve. Only topmostlayer 11 is shown in the figure. As discussed earlier, this is anantiferromagnetic layer which is normally oriented by heating in atransverse (normal to the plane of the figure) magnetic field at atemperature that is at or above its blocking temperature or thatproduces a phase transition into an ordered antiferromagnet in thepresence of a field. The blocking temperature is defined as thetemperature at which exchange coupling between the antiferromagnet andthe ferromagnet goes to zero. Our preferred materials for layer 11 havebeen any one of PtMn, NiMn, PtPdMn, PtCrMn, and NiFeMn, corresponding toa blocking temperature of between about 250 and 350° C., depending onthe choice of antiferromagnet. The thickness of layer 11 would normallybe between about 80 and 200 Angstroms, also depending on the choice ofantiferromagnet. For these ordered phase antiferromagnets, typicalanneal temperatures range from 220 to 300° C.

As seen in FIG. 2, layer 11 has ben shaped (using ion milling) so thatit has two opposing sides 25 that slope downwards away from centralhorizontal area 24. Following conventional procedures, plugs 16 ofmagnetic hard bias material are formed on sloping sides 25. Plugs 16 arepatterned so that they are separated by gap 13 ( between about 0.15 and0.5 microns wide), as seen in FIG. 1. Next, capping layer 17 isdeposited and then patterned so as to be limited to central area 24.

Now follows a key novel feature of the invention. This is the depositiononto hard bias plugs 16 and capping layer 17 of additionalantiferromagnetic layer 21. Layer 21 has a thickness between about 40and 200 Angstroms and can be composed of material such as IrMn, FeMn,RuRhMn, or RhMn, which materials have a blocking temperature that isless than that of layer 11 (typically between about 180 and 250° C.).Alternatively layer 21 may be made of the same, or similar, material aslayer 11, as will be discussed in more detail below.

The last layer to be deposited is conductive lead layer 12. Layers 12and 21 are then treated as a single laminate and patterned together toform gap 28. Because of the presence of layer 21 directly below the leadlayer, the longitudinal bias provided by plugs 16 extends withoutattenuation right up to the edges of gap 28 (see dead zones 15 b). Inthis way the physical and magnetic widths of the device are essentiallyidentical.

Referring now to FIG. 3, we show there an alternative embodiment of theinvention, in which an additional layer, ferromagnetic layer 31 isintroduced. This layer is typically between about 10 and 100 Angstromsthick and may be made of any of several soft magnetic materials such asNiFe, Co, CoFe, Ni, or Fe. Its purpose is to provide improved exchangecoupling between layers 15 and 21.

Finally, the necessary annealing steps that must be taken to ensurecorrect magnetic orientations of layers 11 and 21. For the first casementioned earlier (layer 11 has a higher blocking temperature than layer21) the structure is first heated at a temperature between about 220 and300° C. for between about 1 and 10 hours in a magnetic field of betweenabout 2 and 10 kOe, appropriately oriented, followed by heating at atemperature between about 180 and 250° C. for between about 0.5 and 5hours in a magnetic field of between about 0.5 and 10 kOe (againappropriately oriented).

For the second case mentioned above (layers 11 and 21 have similarblocking temperatures), a proper annealing sequence can be utilized toachieve transverse orientation for layer 11 and longitudinal orientationfor layer 21. In this sequence, layer 21 is annealed into an orderedphase at a temperature lower than the blocking temperature of layer 11.For example, the structure is first heated at a temperature betweenabout 220 and 300° C. for between about 60 and 600 minutes in atransverse magnetic field of between about 2,500 and 10,000 Oe followedby heating at a temperature between about 180 and 250° C. for betweenabout 30 and 300 minutes in a longitudinal magnetic field of betweenabout 500 and 10,000 Oe.

We conclude by noting that the device described above may be fabricatedusing conventional bottom spin valve and contiguous hard bias processes.Among the advantages of this design are the reduction of side reading inthe lead overlap region which is a potential problem for narrow trackwidths. It also will serve to reduce the tolerances associated with theactual size of the GMR device and the misalignment between the leadoverlay mask and hard bias plugs mask. We also note that the patterningof the antiferromagnetic and lead layers can be accomplished by liftoffor by full film deposition followed by patterned etching.

1. A magnetic read head, comprising: a bottom spin valve, whose topmostlayer is a first antiferromagnetic layer, having two opposing sides thatslope downwards away from a central horizontal area; on said slopingsides, two opposing plugs of magnetic hard bias material separated by afirst gap; in said central area, on said first antiferromagnetic layer,a capping layer; on said hard bias plugs and said capping layer, alaminate of a conductive lead layer on a second antiferromagnetic layer;and a second gap, in said laminate, centrally located over said centralarea, said second gap being narrower than said first gap.
 2. The readhead described in claim 1 wherein said first antiferromagnetic layer isselected from the group consisting of PtMn, NiMn, PtPdMn, PtCrMn, andNiFeMn.
 3. The read head described in claim 1 wherein said firstantiferromagnetic layer has a thickness between about 40 and 200Angstroms.
 4. The read head described in claim 1 wherein said secondantiferromagnetic layer is selected from the group consisting of lrMn,FeMn, RuRhMn, and RhMn.
 5. The read head described in claim 1 whereinsaid first and second antiferromagnetic layers are selected from thegroup consisting of PtMn, NiMn, PtPdMn, PtCrMn, and NiFeMn.
 6. The readhead described in claim 1 wherein said second antiferromagnetic layerhas a thickness between about 40 and 200 Angstroms.
 7. The read headdescribed in claim 1 wherein said first gap is between about 0.15 and0.5 microns.
 8. The read head described in claim 1 wherein said secondgap is between about 0.02 and 0.2 microns.
 9. A magnetic read head,comprising: a bottom spin valve, whose topmost layer is a firstantiferromagnetic layer, having two opposing sides that slope downwardsaway from a central horizontal area; on said sloping sides, two opposingplugs of magnetic hard bias material separated by a first gap; in saidcentral area, on said first antiferromagnetic layer, a capping layer; onsaid hard bias plugs, a layer of ferromagnetic material; on said layerof ferromagnetic material and said capping layer, a laminate of aconductive lead layer on a second antiferromagnetic layer; and a secondgap, in said laminate, centrally located over said central area, saidsecond gap being narrower than said first gap.
 10. The read headdescribed in claim 9 wherein said ferromagnetic layer is selected fromthe group consisting of NiFe, Co, CoFe, Ni, and Fe.
 11. The read headdescribed in claim 9 wherein said ferromagnetic layer has a thicknessbetween about 10 and 100 Angstroms.